The present invention relates to a rail gun for accelerating a projectile by a plasma armature generated in an acceleration channel defined by at least two electrical conductor rails.
In a simple embodiment, conventional rail guns are composed of two parallel arranged current-conducting rails which are connected with a high-intensity current source. To accelerate the projectiles, the trailing end of the projectile has an armature that acts as a current bridge between the two rails. An article by R. A. Marshall et al, entitled "The 10 km/s, 10 kg Railgun", in IEEE Transactions on Magnetics, Vol. 27, pages 21 et seq., discloses the use of a plasma which constitutes the armature (plasma armature) and which is generated by an electric arc. The current then flows from the high-intensity current source through one rail and through the electric arc to the other rail which returns the current to the high-intensity current source. The interaction of the magnetic field generated in this current loop with the arc current causes an electromagnetic force (Lorentz force) which accelerates the arc and thus also accelerates the projectile in front of the arc.
In principle, projectiles may be accelerated to significantly greater velocities in rail guns than in gas guns. The above-noted article by Marshall et al indicates, however, that the formation of parasitic electric arcs observed at high projectile velocities leads to a velocity limitation of about 6 km/s.
An article by S. Usuba et al entitled "Performance of the Discrete Electrode Railgun", in IEEE Transactions on Magnetics, Vol. 27, pages 611 et seq. discloses a suppression of parasitic arcs by dividing at least one of the current rails into discrete electrodes. Once the arc has burnt for a length of time on a rearward discrete electrode, the current flow in that electrode is discontinued by means a fuse isolating that part of the current rail. The arc then fires on the next following electrode in the direction of acceleration and is subsequently switched off with the aid of a fuse. This process is repeated until the projectile has left the rail gun.
It is a drawback of the device described in the Usuba et al article that a considerable amount of energy must be generated to commutate the current from one fuse to the next. This is so, because the relatively large current loops formed by the fuses and the current rail must be charged with magnetic energy, which requires the generation of a high reactive and high active power. A further disadvantage resides in the fact that the fuses must be matched very precisely to the acceleration process and the generated currents. Thus, in case of a mismatch, the fuses may respond too early or too late if they respond at all.